I have set up my MX servers to receive incoming connections to port 25 using TLS. I have tested the TLS connections and it is handling incoming TLS connections for inbound email without any problem.

Now, I would like to make sure my MX servers connect to a certain domain (eg visa.com) using TLS connection for outbound emails, i.e. delivering emails from my MX servers to the MX servers of visa.com. How can I make sure my MX servers use TLS connection when delivering email to the visa.com domain?